Yes, Zeus, I was talking about individual systems.
As for geothermal I guess I was speaking to a megasystem while Gerry was speaking about a microsystem for home heating. Home geothermal involves the use of a heat pump to heat a home. It extracts heat from the ground in the winter and pumps it back in in the summer. A friend in Wisconsin is a ground water geologist. He heats his home with heat extracted from ground water. He states you need 3 gal/min. flow in the well to make it work. There are problems if too many people pump from the same aquifer. You need a place to discharge the water after it runs through the system. Then there is the cost of pumping the water.